Such injectors are regularly used by persons who do not have formal medical training. Accordingly, the application comes along with circumstances that set a number of requirements for drug delivery devices of this kind. In case of improper use such as unauthorized disassembly actions there is the risk of contamination of the medicament stored in the cartridge. Also mechanical parts of the device could be damaged. Therefore, the device must be robust in construction in order to prevent fatal manipulation of the components. Especially with regard to the cartridge holder, which is connected to the housing of the drug delivery device, there is demand for a reliable connection easy to manufacture and to assemble but also safe regarding to any kind of manipulation.
US 2001/0034507 A1 discloses a cartridge holder in which a cartridge is accommodated, the cartridge holder being mechanically coupled to a sleeve-shaped mechanism holder by means of a bayonet lock. The cartridge holder shown in EP 1 855 743 B1 is provided with snap fastening connection means to couple a sleeve-like cartridge holder to a housing. The fastening connection means include a pair of apertures provided in the wall of the sleeve-like cartridge holder at a section facing the housing of the drug delivery device and for receiving a locking element of the housing. The apertures are formed as rectangular windows continuously reaching through the cartridge holder. However, rectangular windows generally have walls intersecting at an angle of 90°, which means they have acute-angled edges, respectively corners. In case of improper use or unauthorized disassembly efforts, e.g. by trying to pull or lever out the cartridge holder from the housing, mechanical pressures in the material, especially in the connection means area arise. As a result of the sharp edges and corners of the windows, notch effects occur that cause local stress concentrations in the corner area. Often, plastic materials are used for producing drug delivery devices. Especially at low temperatures, materials of this kind can tend to become brittle. In this case, the concentrated stress distribution in the corner area may result in tear or breakage of the window geometry and the material surrounding the window.